Synthesis, structure and benzannulation of chalcogen-tethered Fischer carbene complexes

Abstract

Addition of PhSH–NEt 3 or PhSeNa to Ph C C C(OC 2H 5) M(CO) 5 [M = Cr or W] afforded stable, β-chalcogenide tethered conjugated carbene complexes 3– 6 as a mixture of E,Z-isomers. The Z-configuration was ascribed to those isomers that readily yield cyclometallated complexes. Aminolysis with methylamine yielded corresponding amino carbene complexes as mixtures of E,Z-isomers. Alkylation by methyl iodide afforded separable E,Z-isomers of dimethylamino complexes. One-step aminolysis of ethoxy carbene complexes with dimethylamine furnished only the Z-isomer of the dimethylamino complex. The Z-isomer of dimethylamino carbene complexes yielded cyclometallated products on warming. Representative crystal structures of these complexes confirm isomer assignments. Only E-isomers of the S or Se-tethered ethoxy complexes undergo benzannulation reaction with alkynes, with loss of chalcogenide atom.